1. Field of the Invention
The invention relates to a blood pressure monitoring system in fields requiring continuous blood pressure monitoring of a patient in an operating room, an intensive care unit, a first-aid room, an extracorporeal dialysis room, and the like. More particularly, the invention is directed to a blood pressure monitoring system utilizing pulse wave propagation time.
2. Related Art
To monitor the blood pressure of a subject by continuously measuring his or her blood pressure, the following methods have heretofore been available. An oscillometric, noninvasive method is designed to measure blood pressure by wrapping a cuff to the upper part of an arm of the subject. A direct, invasive method is designed to measure blood pressure by puncturing an artery of the subject.
By the way, the noninvasive blood pressure measuring method using the cuff may, in some cases, overlook a drastic change in blood pressure due to a shock when the measuring cycle in fixed time measurement is long (e.g., when the measuring cycle is set to 5 minutes or more).
If the measuring cycle is reduced to, e.g., 1 minute to overcome this problem, the blood vessel around which the cuff is wrapped is burdened, which in turn imposes the problem of causing internal hemorrhage.
Further, in the case of fixed time measurement, frequently applied cuff wrapping force that is more than necessary burdens the patient, and therefore causes somnipathy and the like.
On the other hand, the direct, invasive blood pressure measurement not only gives the subject a mental burden due to invasion or brings about the problem of infection, but also gives too much work to the medical staff by involving more labor than in noninvasive blood pressure measurement.
The invention has been proposed to overcome these problems encountered by the conventional art. Accordingly, the object of the invention is to provide a blood pressure monitoring system capable of monitoring the blood pressure of a subject continuously in safety without burdening the subject.
A blood pressure monitoring system based on the aforementioned measurement principle of the invention includes: a blood pressure measurement means for measuring blood pressure using a cuff, a memory for storing an externally inputted pulse wave propagation time fluctuation threshold; a time interval detection reference point detection means for detecting a time interval detection reference point in a pulse wave on the side of aortae of a living organism; a pulse wave detection means for detecting a pulse wave on the side of peripheral blood vessels appearing with a time lag with respect to the pulse wave on the side of aortae; a pulse wave propagation time measurement section for measuring a pulse wave propagation time based on respective detected outputs from the time interval detection reference point detection means and the pulse wave detection means; an operation means for calculating a pulse wave propagation fluctuation from two measured pulse wave propagation times; a judgment means for judging whether or not the calculated pulse wave propagation time fluctuation exceeds the pulse wave propagation time fluctuation threshold read from the memory; and a control means for controlling the blood pressure measurement means based on an output of the judgment means so that the blood pressure of a subject is measured using the cuff.
Further, a blood pressure monitoring system of the invention includes: a blood pressure measurement means for measuring blood pressure using a cuff; a memory for storing a pulse wave propagation time fluctuation threshold and a blood pressure fluctuation threshold, the thresholds being inputted from an external means; a time interval detection reference point detection means for detecting a time interval detection reference point in a pulse wave on the side of aortae of a living organism; a pulse wave detection means for detecting a pulse wave on the side of peripheral blood vessels appearing with a time lag with respect to the pulse wave on the side of aortae; a pulse wave propagation time measurement section for measuring a pulse wave propagation time based on respective detected outputs from the time interval detection reference point detection means and the pulse wave detection means; a first operation means for calculating a pulse wave propagation time fluctuation from two measured pulse wave propagation times; a second operation means for calculating constants inherent in a subject by dividing a difference between two blood pressure values obtained by the blood pressure measurement means by a difference between the two measured pulse wave propagation times; a third operation means for updating the pulse wave propagation time fluctuation threshold within the memory by dividing the blood pressure fluctuation threshold read from the memory by the calculated constants inherent in the subject; a first control means for controlling the operation of updating the pulse wave propagation time fluctuation threshold; a judgment means for judging whether or not the calculated pulse wave propagation time fluctuation exceeds the pulse wave propagation time fluctuation threshold read from the memory; and a second control means for controlling the blood pressure measurement means based on an output of the judgment means so that the blood pressure of the subject is measured using the cuff.
According to the present invention, the blood pressure of a subject can be measured by measuring a pulse wave propagation time fluctuation and consecutively judging whether or not the measured pulse wave propagation time fluctuation exceeds a pulse wave propagation time fluctuation threshold. As long as the blood pressure is measured correctly using the cuff when the pulse wave propagation time fluctuation has exceeded the pulse wave propagation time fluctuation threshold, burdens given to the subject can be minimized.
Further, according to the present invention, the pulse wave propagation time fluctuation threshold is updated. Therefore, the operation of monitoring the blood pressure of the subject can be performed more accurately.